In addition to the traditional test methods, numerical simulation the combustion process of internal combustion engine based on experiment, which have the advantages of short period, fast result, low cost and huge Information, has been an important means to study the flow field of engine and the effect of flow field to the emissions. The combustion process and emission characteristics of DI diesel were calculated using CFD software – FIRE. Some important research information, including the distribution of temperature field and exhaust emission concentration as well as the course of emission growth, were got and analyzed detailedly as a predictable reference for improving the structures and emission characteristics of existing DI diesel and developing the new combustion systems.